Note the old animation system is not removed from JME3.3 yet but deprecated. So you can yet use it if you want to stick with the old animation system. In this case, you should first convert your Gltf models into j3o using JME 3.2, then you can load the j3o in JME 3.3 and use animations as you were using before.
For now, the only documentation we have for the new animation system is this:
and some examples here:
I think we are going to have some more examples in JME 3.3.1 release: